1. Field of the Invention
This invention relates to a two channel pseudo play-back apparatus for pseudo reproduction of a multi-channel audio output, and particularly relates to a two channel pseudo play-back apparatus in a personal computer for pseudo reproduction by two channel speakers of multiple channel audio outputs from, for example, DVD-ROMs.
2. Background Art
Conventionally, in a personal computer loaded with a reproducible sound board of sound or music, it was standard to use two channels for outputting an audio output of the medium for playing back.
Examples of reproducible mediums of sound or music in a personal computer include CD-ROM or CD-I (Compact Disc-Interactive). In the play-back of CD-I, there is a system which is capable of obtaining particular sound effect by processing audio signals for right and left channels, as disclosed in Japanese Patent Application, First Publication No. Hei 2-261213. This apparatus is provided with a function for producing particular sound effects using a four-channel mixing circuit and this apparatus comprises a digital audio processing portion containing a four-times over sampling type digital filter, and outputs two channel audio signals using the four channel mixing circuit by individually processing digital audio data for the L channel and the R channel.
Recently, attention has been attracted to an audio data signal system for digital video discs (hereinafter called DVD), which is a high efficiency coding system of AC-3 developed by Dolby Research Institute in the United States. This AC-3 is capable of playing back 5.1 channels of surrounding sounds. The number of channels in this AC-3 system is defined as two right and left front channels, one front center channel, two rear channels, and a low band channel (0.1 channel) for driving a super woofer.
For such audio data of 5.1 channels are reproduced by a personal computer with two audio output channels, two methods are known as described hereinafter.
A stereo play-back apparatus using the first method is described hereinafter with reference to FIG. 4. The first method comprises the steps of reading compressed digital audio data from a digital video disc-read only memory (DVD-ROM) 11 which stores the compressed audio data, and expanding the compressed data into 5.1 channel audio data by a decoder 12 of the AC-3, and storing expanded data temporarily in a buffer 13 composed of a plurality of buffers 131 to 136. Subsequently, among digital audio data stored in the buffer 13, digital audio data (FR and FL) for the left and right front channels are converted into analog audio signals by respective D/A converters constituted by a left D/A converter (L) and a right D/A converter (R), and thus converted analog signals are output into the audio signal output lines for playing back by left and right speakers 17 and 18.
A stereo play-back apparatus using the second method is described hereinafter with reference to FIG. 5. The same reference numerals are used in FIG. 5 for the same elements as those of FIG. 4, and explanations of the same elements are omitted. The stereo play-back apparatus using the second method comprises the same steps as those described referring to FIG. 4, that is, reading compressed digital audio data from the DVD-ROM, expanding the compressed data into digital signals for 5.1 channels using the AC-3 decoder 12, and storing the expanded data temporarily in the buffer 13. The steps are followed by mixing audio data for 3.1 channels containing the left front channel (FL), left rear channel (RL), the front center (FC), and a super woofer (SU) using a left mixing circuit (L) 18, converting the mixed data into analog data using a left D/A converter (L) 15, outputting the analog data into the left audio outputting line for play-back of the sound by a left speaker 19. Similarly, the audio data for 3.1 channels containing the right front channel (FR), right rear channel (RR), the front center channel (FC), and the super woofer (SU) are mixed using a right mixing circuit (R) 19, the mixed data are converted into an analog signals using a right D/A converter (R) 15, and the analog signals are output to a right outputting line for play-back using a right speaker 17.
In the first method, since audio data for only two channels consisting of the left and right channels (FL and FR) from among 5.1 channels are output, it is not expected to take advantage of the surround effect of the DVD. The second method is able to produce audio quality which is superior to that of the first method by mixing all of the audio data for the 5.1 channels. However, the surround effect of the second method is still inferior to that reproduced by the play-back apparatus for DVD.
Therefore, it is an object of the present invention to provide a pseudo stereo play-back apparatus with two channel speakers, which is capable of playing back a superior surround effect which is not obtainable using a usual two-channel play-back apparatus by processing the multiple channel audio outputs from a recording medium such as DVD-ROM for the two channel audio outputting apparatus.
Another object of the present invention is to provide a pseudo stereo play-back apparatus with two channel speakers, which is capable of playing back a superior surround effect which cannot be obtained with the usual two channel audio output apparatus by pseudo reproduction of the multiple channels by a two channel audio apparatus from a recording medium containing multiple channel audio outputs.